where \(\mathbf {z}_{target}\)  can be an instance in the training set or the test set.
When \(\mathbf {z}_{target} = \mathbf {z}_{i} \in \mathcal {D}\) , memorization can be defined as self-influence [1]}:
\( \mathcal {I}( \mathbf {z}_{i}, \mathbf {z}_{i} ; \mathcal {D}) :=\mathcal {L}( f_{ \mathcal {D}\backslash \lbrace  \mathbf {z}_{i}\rbrace }, \mathbf {z}_{i}) - \mathcal {L}(f_{\mathcal {D}}, \mathbf {z}_{i}) \,.\) 
